Ken's
Electrostatic Wurlitzers

As this website admirably
demonstrates, Ken Griffin was one of America's most popular entertainers,
and perhaps the most widely known American organist.Although there is much information about Ken, the man, and his
playing, I will address an entirely different aspect of Ken's music; the
instruments he played.

To say that Ken's playing is
distinctive is an understatement.Although
seemingly simple, his unique sounds are extremely difficult to copy
accurately.Many people have
tried to imitate Ken Griffin, and although many musicians can play more
elaborate arrangements, Ken's direct, straight-forward playing is a real
challenge for anyone to copy.Most
who try to do so ultimately sound not like Ken, but like people trying
to sound like Ken Griffin.To
imitate Ken successfully requires a surprisingly good and accurate
keyboard technique, and even more importantly, it also requires the
specific instruments which he used, along with some interesting auxiliary
equipment and some specialized recording techniques.

Although
I have not heard every single recording that Ken Griffin made, it seems
safe to say that the major portion of his work was done on two instruments
of his era, the tonewheel Hammond organ, and the electrostatic Wurlitzer
organ.Although the Hammond
is widely known, and indeed Ken did most of his work on the Hammond, he
also used the electrostatic Wurlitzer for perhaps ten to fifteen percent
of his musical output, including one entire LP record, 67 Melody Lane.The Wurlitzer electrostatic organ was also the instrument which he
used on his TV show by the same name.

Some
Basics

It is not my intention to delve
in detail into esoteric electric or electronic or musical principles and
theory here, but there are a few basic concepts which are really helpful
to understand.I will assume
that those of you reading this have at least a cursory knowledge of the
organ as a musical instrument, both pipe and electronic.

One key concept to understand is
that any soundwave can be converted into an analog electrical
equivalent wave, and that such an electrical wave is always an alternating
current.It is also
necessary to realize that many different, various frequency alternating
currents representing, for example, all the instrument sounds of a big
symphony orchestra (or all the notes of multi-note chords and multiple
stops on an electronic or pipe organ) can be combined into a single,
complex alternating current.

This complex current accurately
conveys all of the individual tones, timbres and pitches of the orchestra
or organ to a speaker through a single circuit consisting of only two
wires.(Four if two-channel
stereo.) Furthermore, since this complex signal is alternating current, we
can step it up or down with transformers, we can make it flow around in
capacitive circuits, and it can transmit power.We can also amplify, attenuate, and phase-shift it just like
industry does with standard alternating current power.

Most circuits, components and
systems in both electronic organs and also stereo and hi-fi analog and
digital music systems use unidirectional or direct current for their
operation.It is, therefore,
not only possible but commonplace to find both a DC operating
voltage and also an AC audio signal voltage present in the same
circuit, wire or component as we shall soon see.

What a particular musical tone
sounds like to us as listeners depends on the presence or absence of
particular harmonics and also non-harmonic partials in the
actual soundwave.A harmonic
is a pure tone whose frequency is an integral multiple of the frequency
of the basic musical tone in question.A partial is similar, but its frequency is not an integral
multiple of the musical tone of interest.A second important determinant of the sound of a musical tone is
the way in which it begins and ends.

For instance, a note on a piano
begins loudly very suddenly, drops fairly quickly at first, then continues
to fade away gradually.There
is also a soft but audible "clack" or slight thud just as the
hammer first contacts the one, two, or three strings for a particular
note.The tone of many higher piano tones is not too different from
the higher tones of a flute, but a flute's tone starts only moderately
quickly and likewise stops moderately quickly, and while sounding,
maintains a fairly uniform volume.There
may also be a slight "chirp" or chiff right at the beginning of
some flute tones.

The tonal impressions that we
get from the higher pitches of a flute, and the higher notes on a piano
are therefore completely different to us and we have no difficulty
differentiating them.Still
another aspect is the presence of transients, or short duration
extra harmonics, partials or even extraneous noises that usually occur at
the onset of a musical tone.[The
chiff at the onset of some flute notes, and the hammer noise of a piano
are good examples of this.] Various electronic organs may simulate some or
all of these characteristics to provide facsimiles of different instrument
sounds.Modern digital
synthesizers reproduce these effects extremely accurately.

Vibrato
is a periodic and regularly occurring wavering in a musical tone.It is present in the voices of all good singers, and many musicians
incorporate it into their instrument playing as well.Vibrato is actually a slight changing of the instantaneous pitch
of a musical tone, done so that the pitch varies smoothly both a little
above and below the intended pitch.The
average pitch over time remains unchanged; but the instantaneous pitch is
constantly changing.

Tremolo
is a periodic and regularly occurring variation in the loudness of
a musical tone, without any change in pitch.Of the two effects, vibrato is far more appealing and
desirable.Both vibrato and
tremolo may occur simultaneously, and both sound best when they occur
between 360 to 420 times per minute, or 6 to 7 times per second.

Celesting
or chorusing is a subtle, gentle wavering or undulation which
sometimes creates the illusion of motion in musical tones and occurs when
two or more tones having very nearly (but not exactly) the same
frequencies sound together.In
some modern digital electronic instruments the maker may use the term
"ambience" or "ensemble" for this effect.Such an effect adds life and richness to music, and is present in
virtually all situations where a number of singers or musicians perform
together.It is also present
in most polyphonic musical instruments.Pianos, with their three-strings-per-note for all midrange and
higher notes are another good example of this.

To be successful, celesting or
chorusing frequencies must be very close in pitch.If the pitch difference exceeds a certain somewhat subjective
point, the individual tones begin to sound out-of-tune with each other,
which in fact they are.The
degree of out-of-tuneness which is tolerable is frequency dependent.As frequencies become higher pitched, the differences between them
become smaller and smaller in order to produce acceptable chorusing or
celesting without sounding out-of-tune.

Phasing
of electrical or soundwaves refers to where they are at any instant over
time with reference to a starting position, or to each other.The best way to illustrate phase is by means of a simple
diagram, which shows three identical soundwaves of the same pitch,
amplitude(loudness) and timbre.In
this case, we will use simple sine waves to illustrate the concept of
phase.In the diagram, we have referenced the waves to a circle.The red wave starts at our zero reference at the intersection of
the horizontal (time) and vertical (amplitude) axes.

Notice
that the green wave has already reached its positive maximum when the red
wave is just starting.By
referring to the circle at the left, we see that the dotted line goes to
the +90º position.We
therefore say that in this diagram, the green wave is 90 degrees out of
phase with the red wave, and that its phase is leading, because in time,
it is ahead of the red wave.

Likewise,
the blue wave is still returning from the negative side of the base line
and doesn’t reach the (zero) starting point until the red wave has
already reached its positive peak and is starting to decrease.Therefore, referring to the circle again, we see that the blue wave
is 90 degrees out of phase with the red wave, and its phase is lagging,
because in time, it is following behind the red wave.Likewise, we see that the difference or span between +90º and
–90º is 180º and therefore in this diagram the green and blue waves
are 180º out of phase with each other.Phase difference is typically expressed by degrees, which the
reference to the circle makes very easy to see.Phase difference can be any whole or fractional number of degrees
lagging or leading.I chose
to use ninety degrees here to make the example easy to understand, and
easy for me to draw!

When
a wave gradually either advances or retards in phase
in real time, this changing of phase is also accompanied by a change in
frequency.If a wave
undergoes a full 360º phase change in one second, there will be a
frequency shift of one cycle per second.If the wave advances in phase, the frequency will increase by one
cycle per second.If the wave
retards in phase, there will be a decrease of one cycle per second.Likewise, if, for example, the wave changes by 3600º in one
second, (ten times around the circle) there will be a ten cycles per
second change in frequency.This frequency change occurs only while the phase of the
wave is changing.As soon
as the wave stops changing in phase, the frequency will once again be
whatever it was before.

This
concept of real-time phase changing and resulting frequency change is very
important when we consider the means in which both the Hammond organ and
also the Wurlitzer organ produce their respective vibrato effects.Both instruments use continuous phase changing (both lagging and
leading) to create their pitch-varying vibratos.

Introduction

There
were essentially two operating principles for electronic organs of Ken's
time; keyed-audio, and keyed-generators.In the first category of keyed-audio there are two
sub-categories, that of direct-keyed audio and electronically-keyed
audio.All electronic organ
tones, regardless of the operating principle, originate in an assembly
known as a tone generator, essentially a device for generating or
providing numerous alternating currents whose frequencies are those of the
individual keys and pedals of the instrument.In either type of keyed-audio system, the alternating currents
representing the audio or actual tones are available as long as the
instrument is turned on.The
keys and pedals then switch the appropriate audio AC voltages to the
voicing circuitry and ultimately to the amplifiers and speakers of the
instrument.

In a direct-keyed
audio system, the audio signal voltages are present on the actual key
and pedal switch contact assemblies.In the electronically keyed audio system, the audio signals
are present at the inputs of keying or gating circuits.The gating circuits are controlled by the key contacts of the
manuals and pedals of the instrument.

In the keyed-generator
system, the tone generators are normally inoperative, and will only
produce their audio AC voltages when they are turned on, or keyed, usually
with a DC voltage, by the playing keys and pedals of the instrument.The Hammond tonewheel organs of Ken's time operate on the direct
keyed-audio system, and the electrostatic Wurlitzer organs are
keyed-generator instruments.Many
of the more modern electronic organs, including the newer, non-tonewheel
Hammonds use the electronically-keyed audio system.Also, the touch-response percussion of the B3 is an example of
electronically keyed audio.

As we
said, the majority of Ken's musical work was played on Hammonds, but we
will consider the electrostatic Wurlitzer first.This is the instrument he used exclusively on 67 Melody Lane,
both the record album and his TV show by the same name.He also used it on a number of selections on his other recordings,
notably September Song, Far Away Places, Love Letters in the Sand,
Dream, My Dreams are Getting Better All the Time, I want to Be Happy,
Teardrops on My Pillow, Valencia, The Nearness of You, Moonbeams,September
in the Rain,Somebody Else is Taking My Place, You Are My
Sunshine,Marcheta, and I Don't Want to Set the World on
Fire.

In addition to the above, Ken made a series of radio transcription
recordings during the early 1950s.I
do not know exactly when he made these recordings or how generally they
were distributed.They were
originally recorded on special very large diameter LP records which cannot
be played on ordinary turntables, and I consider myself very fortunate to
have been presented with a set of three cassettes which were made from
these original special discs.On
these radio transcriptions, Ken used the Wurlitzer electrostatic organ for
a number of selections.Of
the three radio transcription cassettes that I have, the Wurlitzer
occupies roughly 70 percent of the total playing time on one of these
cassettes.Ken may also have used the Wurlitzer on other recordings, but
I do not know this with certainty as I have not yet heard all of Ken
Griffin's recordings.

The
electrostatic Wurlitzer is a unique and completely different instrument
from any other electronic organ.From
its very distinctive sounds to its operating principle, it is definitely
in a class all by itself.In
complete contrast to the wealth of information to be found on the Internet
about Hammonds, I have found virtually nothing about these instruments,
therefore, I will elaborate significantly on this most unusual electronic
organ.

This
next picture, figure 2, shows a general view of a Wurlitzer electrostatic
organ, and the inset is a closer view of its stop rail, which appears to
be very similar to the stop rails of many other electronic organs of the
1950s and 60s.Compare this
with several pictures in Bill Reid's listing of the Ken Griffin records
that he has.Here you'll see
several pictures of the electrostatic Wurlitzer that Ken used on these
albums.

I must now preface my remarks with a notice that
in many places in this Ken Griffin website, you will see the Wurlitzer
instrument referred to by myself and other contributors as the ES organ or
Wurlitzer ES.This is simply
the abbreviation for the word electrostatic.Also, it is the term we of the Ken website have adopted for
the instrument although it is not original with us.These organs were not called or marketed by Wurlitzer as ES
organs.We choose to call
them that because they operate on the principle of the electrostatic
transducer which we will explain shortly.In like manner, we refer to Hammond organs of that era as tonewheel
organs, again because of their operating principle.

Wurlitzer's actual model
designations for these organs, which were built in the period from roughly
1946 to 1961, were the 4400 series, 4600 series, and 4800 series
instruments.Ken, as far as
we know, used various 4601 models.The
one which I have used for some of my Ken Griffin imitations, and from
which these and subsequent pictures were taken is a model 4602.The 4400 series are spinets, of which the 4410 and 4450 were sold
in relatively large numbers.The
4800 series models are thirty-two pedal concert organs with liturgical
voicing and stop nomenclature.The
4601 is a 25 pedal console designed for pops playing.The 4602 is a 32 pedal version of the 4601 console with more
classical stop nomenclature.The
4601 and 4602 are very similar in general appearance and also internally,
but with some differences in stop designation and amplification.

The
electrostatic Wurlitzer is sometimes called a Wurlitzer reed organ, or an
amplified reed organ.Both of
these names are incorrect, however, because they imply that you hear the
sound of reeds when you play this instrument; an implication which is
absolutely false.It is true,
however, that the electrostatic Wurlitzer organs do contain air-powered
free reeds, one reed for each available frequency.However, everything possible is done so that the actual sound of
the reeds can't be heard.And
indeed, this is a very good thing, for in the electrostatic Wurlitzer, all
of the 73 or 85 reeds (depending on the model) sound at once; and they
sound all the time when the instrument is turned on.A high-speed centrifugal compressor or blower, which is an integral
part of the reed unit, powers this system.

In
order to understand the electrostatic organ, we need first to learn a
little bit about capacitors.In
its simplest form, a capacitor is nothing more than two sheets or plates
of metal, parallel to and close to each other, but separated by either an
air space or else some other insulating material.

If
we connect this elementary capacitor to a source of direct current, such
as a battery as shown in figure 3, for a very brief instant, current will
flow until the plates of the capacitor are fully charged.At this point, no further current will flow, because the plates are
separated from each other.If
we were to disconnect this capacitor from the power source, we would find
that a voltage equal to that of the charging voltage would remain on the
plates.Connecting the two
plates together would very quickly discharge the capacitor and most likely
produce a visible and audible spark.

Now
the general equation for capacitors is this: Q = CE, where Q is the
electrical charge in Coulombs, C is the capacitance in Farads, and E is
the voltage of the power supply.Because
this is an equation, both sides must always equal each other, and any
change to any term must be balanced by a compensating change on the other
side of the equal sign.

The
capacitance (how much of an electrical charge it will hold) of a capacitor
depends among other things on the physical distance between the plates.If we move the plates closer together, the capacitance increases,
and it can hold a bigger charge.Conversely,
if we move the plates away from each other, the capacitance decreases and
it can not hold as much of a charge as it could previously when the plates
were closer together.Of
course the surface area also governs the capacitance.For this example, however, let us assume that the plate size is
fixed.

Let's
now say that we have a certain capacitor, and we have applied a voltage
across it from a battery, and the capacitor is fully charged.I appear on the scene and push the plates closer together.(Naturally, I'm wearing my insulated electrical workers' gloves for
this venture.) Because the capacitance has increased, more current will
flow until the capacitor has taken on a bigger charge.(Holds more electrons.) Now, I decide to see what will happen if I
move the plates away from each other.When I do this, C decreases.The
equation, however, must always balance.Since the battery has constant voltage, then the charge, Q, must
decrease also, and while I am moving the plates apart, current flows from
the capacitor back to the battery until a new, smaller charge (fewer
electrons) exists which is consistent with the new distance between the
plates.

This
says to us that if I provide some means of moving the capacitor's plates
together and then apart, and do this at, say 440 times per second, then a
current will flow into and out of the capacitor, and it will make 440
complete cycles per second.This
further tells us that I could perhaps use this changing current to provide
a musical tone if I can somehow extract it and put it to work.Therefore, I place a load resistor in the circuit as shown
in figure four:

Whenever
a current flows through a resistor, a voltage drop will occur across the
resistor according to well-established electrical laws.Furthermore, the signal voltage that I can get will be alternating,
as the current flows first into and then back out of the capacitor.This AC voltage, however, will in effect be "riding" on
the DC voltage that I must apply to this capacitor in the first place to
charge it so that it can give us the AC signal.Here is a very good example of both DC and AC coexisting in the
same device.

It
is also very important to understand that current cannot flow through
a capacitor.The two plates
are always (by definition) separated from each other; there is no
connection between them.Therefore
current can only flow into or out of a capacitor, but never
through it.If an alternating
current exists in a capacitive circuit, then it will flow around in
the circuit, into and out of the capacitor, but again, never through it.

Nevertheless,
in many ways, an alternating current flowing around in a capacitive
circuit behaves as though it were in fact flowing right through the
device.This concept is important to keep in mind as we get further
into our discussion of the electrostatic Wurlitzer instrument and also the
Hammond.For practical
purposes in our discussions of and thinking about audio signal
applications, we may correctly speak of the AC signals as flowing through
capacitors, because they behave exactly as though they did this.

Capacitors,
by virtue of the above properties, produce a number of other interesting
phenomena, some of which are also utilized in both types of electronic
organs.Of course, if we put
too high a voltage across the plates of a capacitor, the voltage will
cause an arc to form, and then current will jump across and flow, via the
arc, from one plate to the other.Current
will also truly flow through a capacitor if we cause the plates to touch
each other.Both of these are, however, abnormal conditions, and I
mention them as such.For the
purposes of this discussion, we will assume that the voltage will never be
high enough to arc across the plates of any capacitors of any electronic
organs, nor will their plates ever touch.

Now
then, let's return to a capacitor whose plates can move back and forth at
a rapid rate.This implies that if I want, I could use a capacitor whose
plates move closer together and then apart 440 times a second to give us
an alternating current voltage with a frequency of, you guessed it,
standard A440.Furthermore,
if I can get enough friends together, and give each of them a capacitor
along with specific instructions to move their capacitor plates back and
forth at other musical frequencies, I should be able to hook up DC
voltages, a load resistor and finally, a 61 note organ keyboard to all of
these capacitors and utilize the resulting different frequency AC voltages
to drive a speaker and make all the notes of the scale.And this is great.They
do the work, and I get to play!

Now,
keeping a crew of 61 individuals busy shoving capacitor plates back and
forth at rapid rates is somewhat impractical, especially when we'll be
zapping them with high voltage direct current each time I choose to press
a key! (I, of course, am using a keyboard with plastic keys, so I am
insulated from the high voltage DC.)

There
is, nevertheless, a very simple device which can serve the purpose, and
that is the lowly brass free reed, just like those that you find in the
old foot-pump reed organs and in accordions.Reeds are simple, cheap, and, if they are of this so-called free
type, such as those in the aforementioned instruments, they are also
extremely pitch-stable and reliable.

Free
reeds consist of a narrow strip of springy metal such as hard brass, and
also a supporting frame or shallot with a suitable opening over
which the reed strip vibrates when air flows by the reed and through the
opening in the correct direction.In
a free reed, the opening in the shallot is very slightly larger than the
reed itself, and thus the reed strip vibrates into the opening for part of
each cycle.This is why it is
called a free reed, since the vibrating portion of the reed strip doesn't
touch, or is free of, the supporting shallot.In a typical free reed, the clearance between the reed and the
opening into which it vibrates is no more than a few thousandths of an
inch.Free reeds, especially
the small ones that are used for the high frequencies of a keyboard
instrument require a watchmaker's precision in their manufacture and
initial tuning.

Anyhow,
I can use a vibrating brass free reed as one plate of a capacitor.All I need to do then is to get a second plate, and place it close
to the reed, preferably right over it.Now, if I put a DC voltage across the reed and the stationary
plate, I have, (wowser, would you believe?) a capacitor with one of its
plates moving rapidly back and forth.Put a load resistor in the circuit, and there it is: a simple,
stable, and accurate producer of a suitable alternating current that can
become one note on a keyboard or a pedal board of an electronic organ.

It is at this point very important to realize
that this vibrating 'reed' capacitor does not generate any electricity.It simply modulates the charging voltage which exists across it.The modulation of the charging voltage results in a varying
voltage, which when developed across a load resistor and extracted through
an isolation or coupling capacitor (to be described in a little while) is
then an alternating current audio signal which can be amplified, filtered,
phase-shifted, reverberated, sustained or otherwise processed into one
note or tone of an electronic organ.

Note
also that the charging DC voltage either exists or does not exist on the
reed and on the close-proximity stationary plate, however, no direct
current ever flows through the reed-capacitor.It is because there is no current flow through, only a charging
potential across, that we use the term electrostatic, which by
definition means no current flow.In
other words, a static electrical charge can exist across the
reed-capacitor.

Free
reeds produce a characteristic and rather unpleasant sound.You need only listen to an accordion to confirm this.In the Wurlitzer electrostatic organ, however, we're not interested
in the sound of the reeds at all.In
fact, the direct acoustic sound of the reeds is simply a useless
by-product of their operation, and as some of the following pictures and
text will show, elaborate measures are taken to insure that we will never
hear the actual reed sound from these instruments.

What
we are interested in, however, are the possible AC audio voltages which,
as one plate of vibrating variable capacitors, these reeds can provide for
us.In the electrostatic
Wurlitzer, each reed has from one to three separate electrodes called
pickups in close proximity.One
pickup is over the approximate center of the reed.One is directly above the free end or tip of the reed, and the
third is arranged right at the front edge of each reed.

If
we put a DC voltage across the reed and any one of the three pickups, then
together, they will constitute a small capacitor.Since the reed is vibrating, the capacitance is constantly changing
at the reed vibration frequency.When
we put a DC voltage across a pickup and the reed, a current must flow into
and then out of the resulting reed-capacitor as the reed vibration changes
its actual capacitance.This current is, as we already stated, an alternating
current, and it has the same frequency as that of the reed.We can then stick a load resistor in series with the reed,
and every time we zap any pickup of this reed-capacitor with a DC voltage,
we'll get a corresponding AC audio voltage across the resistor.

Free
reeds of this type would be very slow in developing their steady state
output tones if we were going to use them as direct sources of sound and
subsequently keyed the operating air to them.The larger reeds that we would need for organ pedal tones, for
example, can take up to two seconds to reach full acoustical output.This would make such a reed impractical for many types of music,
especially any music with a decided beat and a rhythmic bass pattern such
as the majority of Ken's playing exhibits.This of course was one of the major drawbacks of early reed organs.Furthermore, the tone of free reeds is, as we just mentioned, very
unpleasant; snarling and growling at lower frequencies and wheezy and
keening at higher frequencies.Again,
think of the accordion.There
really is a reason for all those accordion jokes!

However,
when we use such a reed as a variable capacitor in the Wurlitzer
electrostatic organ, we can key it very rapidly, because we're keying
the DC voltage to the pickups, and the reed is always in motion.As long as we keep the reed vibrating mechanically, we can key the
pickups as fast as we want, and the tone will start and stop instantly.Not only that, we can add circuitry to modify the way in which the
keying voltage on the pickups builds up or decays.We can, therefore, use this system to create fast percussive or
slow mellow attacks or onsets to the generated tone, and we can also
introduce percussion sustain, something impossible on either a reed organ
or an accordion.

Another
nice feature of this system is that two of the three resulting tones that
we get by amplifying the AC audio voltage from the three pickups of these
reed-capacitors sound nothing at all like an accordion.Indeed, if we put our pickups over the centers of the reeds, we
will get a soft flutelike tone, very similar to that of the pipe organ
Melodia or concert flute stop.If
we put a pickup above the free, vibrating end of the reed, we get a tone
somewhat like that of a diapason.If
we then place a third pickup so that it looks at the vibrating front edge
of the reed, we get a complex tone with considerable harmonic development
which is good for orchestral reed and string voices.This tone does bear a slight resemblance to the sound of an
accordion but it is nevertheless quite different and has none of the
unpleasantness of accordion sound.

The
heart of the Wurlitzer electrostatic organ is its reed unit, a
hermetically sealed assembly with a bank of 85 reeds (in the 4600 series
console versions) covering the entire pitch range from the low C of the 16
foot pedal stops to the top C of the four-foot flute stops.Here are two views of the interior of the electrostatic Wurlitzer.The first, is a general look inside the console with the back cover
removed.It shows the basic
layout, and as you can see, it looks like any typical 1950s electronic
organ, with a chassis with vacuum tubes at the bottom, and a
self-contained speaker in the center.The reed unit is to the right, just barely visible in this picture.The blower motor is visible on the bracket attached to the side of
the reed unit.

This next picture
shows the reed unit with part of the external soundproofing removed.
The centrifugal blower is plainly visible on the top of the reed unit, and
you can also see the blower drive shaft extending to the left and out
through the side of the soundproof enclosure. The blower motor is
the only part of the reed system that is external to the soundproof
housing. This photo also shows the top portion of three of the seven
reed pans directly below.

All
eighty-five reeds blow at once as long as the instrument is operating.The reeds are arranged by octaves inside these pressed-steel pans
as shown, one octave to each pan.The
pans are lined with eighth-inch thick rubber for sound suppression.Each pan is held in place by three nuts and seats on a gasket, thus
making the system hermetically sealed when all pans are in place.The operating air for the reeds is continually recirculated
inside the reed unit with no exchange of outside air, thus excluding any
dust and dirt from the system.In
addition to sealing the reeds from the outside air, the pans, being steel
and being grounded through their retaining nuts and threaded rods, also
provide electromagnetic and electrostatic shielding which is necessary to
keep away power line and radio and TV interference from the reeds' output
signals.

The entire
reed unit mounts as shown in the soundproof enclosure consisting of an
outside box of 1/2" Homasote, followed by one inch thick heavy felt,
and 3/16" Masonite.This
then gives a total of 5 different layers of material between the reeds and
the outside of the reed unit assembly; rubber, steel, Masonite, felt, and
Homasote.This next photo,
with a little more of the soundproof enclosure removed, shows the other
side of the reed unit and the additional seventh pan on the end.It also shows the steel reinforced construction of the
soundproofing enclosure.

The centrifugal compressor or blower
draws air through the reeds into a chamber behind each group of reeds.The chambers communicate to a central exhaust manifold that
connects to the blower intake assembly in which there is a very fine-mesh
screen.The discharge of the blower enters the high pressure manifold
which feeds the air back into each pan through individual openings fitted
with adjustable slides or gates.Since
the amount of air withdrawn from each pan through the reeds always equals
the amount of air returned to each pan, the interiors of the pans remain
effectively at atmospheric pressure.The reeds, therefore, can be said to operate on suction relative to
the outside world.The reeds
under any pan will continue to operate with a pan removed, which is
necessary should the need arise to adjust the pickups on the reeds.

The direct sound
of the reeds with a pan removed for servicing, particularly those in the
mid-range of the instrument, is really terrible, sounding like a serious
accident at the accordion factory.The
reeds, however, are very small-scale, because they do not have to produce
any acoustic output so it is not unbearably loud.Also, since the reeds vibrate all the time, they are lightly blown
so that they do not vibrate through a very large amplitude.

This low amplitude
vibration is necessary so that they will not weaken over time and snap off
from metal fatigue.The reeds
of a reed organ or an accordion, which instruments depend on the actual
sound of the reeds for their tones, must of necessity make lots of noise
and vibrate at a greater amplitude.Of
course in reed organs and accordions, the reeds do not have to vibrate all
the time, only when called upon to produce a particular note.This is the main function of the adjustable blast gate in each pan;
to limit the total airflow through each group of reeds and keep the
mechanical amplitude of vibration minimal.It also keeps each group of reeds vibrating at a consistent level
with respect to the other groups, so that no one particular group vibrates
too much or too little.

The reeds of the
first or sub-octave group have only one pickup, about two thirds of the
way towards the free end of each reed.These reeds are used only for notes one through twelve of the pedal
16' stops.This next picture
shows a close-up of the pedal 16' reeds.

Other groups of reeds may have
either two or three pickups. In various different models of the
electrostatic Wurlitzer, the pickups over the centers and the tips of the
reeds may have different functions. In some, one pickup is for pedal
tone, in another the center pickup may provide a soft, flutelike tone.
The pickups over the free ends of the reeds are for the normal manual
flute stops, and the pickups at the leading edge of the reed tips generate
the so-called trumpet tone, which is a more or less generic reedy tone
having considerable harmonic development.The very last or top octave group of reeds, labeled octave
number six, generates the top octave of frequencies for the four foot
pitch range and has only one pickup per reed. These pickups are
considered normal flute tone pickups.This next photo shows the next to the highest octave of
reeds, with only two pickups per reed, and as you can see, these treble
reeds are extremely small.

Figure
eleven shows a close-up of the reeds in the third octave of the
instrument. Here, by looking at the top reed, you can see the three
pickups plainly and their relationship to each other and to the reed with
which they are associated. Notice that the front edge pickup is a
flat, slightly bent piece of sheet metal, whereas the other two pickups
are threaded for adjustment. Colored wires attach to terminals held
by the pickup holding screws or nuts on each pickup and are the means by
which the charging DC voltage is applied to the pickups from the keying
networks.

Thus,
most of the reeds can generate two or three different waveforms.Different voices or stops in the electrostatic organ result from
the use of these waveforms individually or in combinations.The instrument also uses additive synthesis, which I will describe
in the Hammond section, to produce the voices of Diapason, Clarinet, and
Oboe.The French horn on the
solo manual and all of the higher pitched manual flute tones come directly
from the pickups over the tips of the reeds.As is typical of a pipe organ, flute pitches are available on the
both the upper and lower manual at 16, 8, 4, and 2 foot pitch levels.In addition, there are two mutation pitches, a 2 2/3' and a 1 3/5'
pitch on the upper manual, and a 2 2/3 pitch on the lower.These correspond approximately to the third and fifth harmonics of
a normal eight foot pitch.Some
models also have pitches of 1 1/3 and even 1' on the lower manual.

There
is also a soft flute stop, called a Flauto Dolce or perhaps Accompaniment
or simply Soft Flute on the lower manual.When this stop alone is on, the keying voltage to the flute pickups
on the reeds is considerably reduced in some versions of the electrostatic
Wurlitzer, and in others, the keying voltages are applied to the center
pickups which give a softer tone than those above the free ends of the
reeds.

Besides
these, there are also stops labeled Trumpet and Salicional on the upper
manual, and Tenor Trumpet and Dulciana on the lower.Most of these are pipe organ stop names.While not sounding really like a trumpet or either a Salicional or
a Dulciana, these four stops take their tone from the pickups which are
affected by the front edges of each reed.As with the Flauto Dolce, the Salicional and Dulciana stops apply a
greatly reduced voltage to the appropriate pickups.

The
front edge pickups are, as stated, flat pieces of sheet metal.Since the edges of both the sheet metal pickups and also the fronts
of the reeds are very narrow, the resulting electrical waves from these
pickups contain sharp spikes, since these edges are in close proximity
twice, but only for a very brief portion of the total time of each reed
vibration cycle, which results in the production of many harmonics.Figure twelve is a diagram of a triple-pickup reed electrostatic
tone generator.

Interestingly
enough, because of the physical relationship of the pickups to the motion
of the reeds, the signals from the front edge pickups are not in phase
with the signals from the pickups over the tops of each reed, but lag them
by approximately eighty to ninety degrees.Thus, if you combine the tones from the front edge pickups with
those of the pickups over the reeds, some of the harmonics in the
resulting mix actually partially cancel out, resulting in a different type
of tone, having somewhat the quality of a clarinet with a strong
fundamental, lots of upper harmonic development and, with the exception of
the fundamental, slightly reduced lower order harmonics.

Another
interesting observation concerns minute differences in the sound or timbre
of the tone from one note to the next when we examine the tones which come
from these front-edge pickups.The
tolerances of adjustment on these pickups are very small, with the
clearance between the front edge of the reed and the edge of the sheet
metal pickup being only around 0.001 inch.Furthermore, exactly where the edge of the pickup is relative to
the reed's arc of vibration influences the timing between the two spikes
that result as the reed passes the front edge pickups first in one
direction and then the other.See
this next diagram which shows how this difference can occur.

In
normal playing and casual listening, the timbre from one note to the next
appears consistent and similar, but careful scrutiny as well as
observation of the waveforms on an oscilloscope shows marked differences.A change up or down of as little as a few thousandths of an inch
can make the tone sound more like a clarinet, or more like a cello as the
timing between the spikes of each cycle of the wave change in time-phase
relative to each other.

Interestingly,
these minute tonal variations are slightly different from one instrument
to another because of minute differences in the adjustments of the
pickups.Really careful analysis allows us to develop an audible
"fingerprint" of a particular instrument.This, by the way, confirms that the instrument which Ken
played on the 67 Melody Lane TV show and on the Columbia LP by the same
name is the same instrument.It
also shows, however, that the one he played on the Columbia LP "You
Can’t be True, Dear," is a different instrument, and likewise the
one he used on the radio transcriptions is still another one.

The
adjustment of the pickups over the centers and the ends of the reeds is
not quite as critical, as the shape of the electrical wave from these
pickups is much simpler than that from the front edge pickups.On some of the reeds, the pickups are inserted into slots instead
of round holes, so that they can be moved closer to the ends or closer to
the centers of the reeds.The
motion of the reed strips at the centers is fairly simple, somewhat like,
but not exactly the same as the motion of a pendulum.At the tips of the reeds, however, the motion is slightly more
complex.The reed strips can
flex a little near the free ends, almost like a ballet dancer flexes her
wrists when simulating the motion of birds' wings, and therefore, from
pickups that are closer to the tips of the reeds we get a strong second
harmonic as well as traces of the next several higher harmonics.

At
the end of the Wurlitzer section of this article I have provided a set of
pictures which illustrates the actual waveforms that are generated by the
various pickups on several different reeds and gives you an idea of what
the sounds "look like." The pictures are marked according to the
note of the scale and also which of the three pickups is producing the
waveform.Notice in
particular, the differences in the waveforms from the front edge pickups
of two adjacent notes, Tenor B (right below Middle C) and Middle C itself.These are from our 4602 console.Actual waveforms observed from Ken's 67 Melody Lane record album
appear very similar.

There
are numerous advantages to this system over the typical reed organ.As I previously mentioned, the tone of free reeds is not very nice
to listen to.Furthermore, it
is so distinctive that it is hard to make a reed organ or an accordion
sound like anything but exactly that; a reed organ or an accordion.Furthermore, the speech characteristic of free reeds is very slow.Originally, an electrostatic electronic organ using free reeds
appeared on the scene in the 1930's.Known as the Orgatron, it had several sets of free reeds with
pickups above the reeds.The
reeds would remain at rest until keyed pneumatically by electromagnetic
pallet valves under each reed.The
instrument looked impressive, with a full-size AGO console and various
stop tabs above the upper manual, but it was generally not a successful
instrument at all.

The
lower pitched reeds spoke so slowly that it was virtually impossible to
play either fast popular music or any classical music having an intricate
pedal figure.To make matters worse, when you let up on a lower pedal note,
the reed continued to vibrate or ring mechanically for a disturbingly long
time.This of course would
generate no more direct acoustical sound, since the operating air was now
cut off, but with the charging voltage always on the pickups of these
early instruments, it would continue to produce an audio signal at the
speakers, thereby making any semblance of pedal definition essentially
unattainable.

The
soundproofing on the reeds of the early Orgatron instruments was also less
than adequate, and a significant portion of the direct sound of each reed
would emanate from the console and detract from the sounds from the
speakers.In fact, on these
early Orgatron instruments, one could play audibly without even turning on
the amplification system, in which case the instrument became simply an
electrically powered reed organ, and a mighty heavy one at that.It also had the additional joy of a really noisy blower that
sounded like a domestic oil-heating boiler on overload.Fortunately, very few of these relics remain in active service
anymore, although I have seen a few in funeral parlors.This is probably not a problem, however, as the principal clients
of funeral parlors are no longer in a position to hear or care how
terrible the instrument is.

The
Wurlitzer electrostatic organ of the type we describe here and that which
Ken Griffin used was, at the very least, a second-generation descendent of
the cumbersome and unmusical Orgatron and had none of its shortcomings.Since the reeds vibrate continuously, there is no lag time.Tones develop when the pickups over the reeds become charged
with DC by pressing keys.Letting
go of a key switches off the DC, and a discharge resistor bleeds the
residual charge off very quickly, so any type of music can be played
successfully.Soundproofing
is very elaborate, so no reed or blower noise ever intrudes on the music,
and the blower itself has an entirely different impeller configuration and
is designed to operate very quietly.It is also a much smaller blower than those which we find in the
Orgatrons.

In the
typical Wurlitzer electrostatic organ, a high voltage direct current (up
to 300 volts) goes through a voltage divider to several busbars running
the length of each manual and also the pedal key switch assembly.Typically, the keying voltage for normal operation is a +160 volt
DC, dropped from +300 by the voltage divider.

Under
each key and pedal are several contact wires, which, when a key or pedal
is depressed, make contact with these busbars.The busbars are made of insulating material however, but each has a
nichrome wire running its length.The
nichrome busbar wires connect to the aforementioned voltage divider.The busbars can rotate through about a sixty degree angle.When a stop is off, the appropriate busbar is in such a
position that the key contacts touch the insulating material and nothing
happens.When a stop is on,
however, the busbar rotates so that the nichrome wire is on the top.Then, pushing any key will allow the appropriate contact to touch
the nichrome wire on the busbar, completing the circuit and allowing the
DC voltage to enter the appropriate keying network for a particular pickup
on the reed for the required pitch and tonality.

The keying networks consist of resistors and capacitors.

These are pedal keyers.The manual keyers are smaller, and the various components for each
manual keyer are all encased in a housing called a couplate.The purpose of these networks is to "shape" the resulting
build up and decay of each keyed tone, so that the tones build almost, but
not quite, instantly, and also that each tone may roll-off or decay,
again, quickly but not instantly upon key release.

This
takes away the inherent "telegraph key" effect which was
prevalent in many electronic organs of the period and makes the overall
response more like that of a typical theater pipe organ.It also essentially eliminates key clicks.Unlike many other instruments of that period, the Wurlitzer
electrostatics sound reasonably acceptable even without any reverberation
effect.Figure fifteen is a schematic of an actual keyer for a
typical reed pickup and shows the small network of capacitors and
resistors that govern the application and removal of the keying voltage
from the pickup.

We should now examine
another function of a capacitor, and that is its ability to store an
electrical charge on its plates. For this purpose, we need to use
fixed or constant value capacitors. Typically, these consist of two
plates made of metal foil with insulating sheets between, above and below
them. To save space, this capacitor "sandwich" consisting
of the two foils and the insulating sheets is rolled up into a small
cylinder, and the whole is then sealed in plastic or some other protective
insulating material. A lead-in wire protrudes from each end of the
sealed casing, each wire connected internally to one of the two rolled-up
foils. Look again at figure 14 of the keyers, where at the bottom of
the picture, you see eighteen black plastic cylinders with colored bands
painted on. These are some of the keyer capacitors, in this instance
associated with the pedals. The colored bands are a code that
identifies the value and value tolerance ratings of these capacitors.

When
we apply the DC keying voltage to a reed pickup, a small portion of that
voltage causes a tiny, brief current to flow and charge the associated
keying capacitor for that particular pickup.As this takes place, the voltage applied to the reed pickup
likewise builds up quickly, but not instantly, since the capacitors are
charged through resistors.A
resistor is simply a device which slows or retards the flow of electric
current.In the picture, the
tiny cylinders directly above each capacitor are the resistors which serve
to slow down or limit this keying current.As a particular keyer capacitor charges, the voltage applied to the
associated reed pickup builds up until it is equal to the voltage (+160
volts DC) coming in from the appropriate key contact and busbar.At the same time, the tone gradually builds up in loudness until it
reaches its maximum when the keying capacitor is fully charged.

When
we release a key or pedal, we remove the source of charging voltage since
the key contact is no longer touching the busbar to receive more +160 volt
DC.The capacitor now begins
to discharge through the resistor, which causes the voltage on the pickup
to decrease gradually rather than to drop abruptly.This causes the signal from that particular reed pickup to decay
correspondingly. In virtually
all real (non-electronic) musical instruments, strings, reeds, struck
bars, drumheads or gongs, or vibrating air columns, the stopping of a tone
actually takes a slight amount of time as the vibration gradually, but not
instantly, decreases. Even
though this stopping may take place in only a few milliseconds, it
nevertheless is not instantaneous, and it is what we come to expect of
every musical sound, be it the horn on a diesel locomotive or a piano
string.The Wurlitzer
electrostatic organ mimics this important characteristic in the manner
that I have just described.

Shortly
after the introduction of the electrostatic organs, Wurlitzer developed a
percussion sustain accessory, which was available either as an original
factory installation or as a later retro-fit for all of the different
versions of the Wurlitzer electrostatic organs with continuously running
reeds.This device contained
extra resistor-capacitor circuitry which could be switched into the keying
circuits by multi contact relays to provide percussion sustain.You can hear Ken use this effect in Far Away Places, September
Song, and The Nearness of You, among others.In this mode, the appropriate reed pickups would become charged
very quickly when you played a key, but this charge would be held by the
sustaining capacitors for several seconds after you let go of a key.As the charge was gradually bled off through the associated
discharge resistors, the tones would then fade away or ring out gradually.

The
beauty of this reed system when used as a variable capacitive tone
generator is that the strengths of the generated tones vary with the
applied DC voltage.If you
insert a means to make the voltage drain off slowly after you let go of a
key, the generated tones will then decay gradually, creating sustain.

A
second and related effect, which was introduced shortly after the sustain
circuitry, consisted of a faster means of applying the voltage to each
reed and keyer network.When in this mode, the electrostatic organ tones would begin
percussively, somewhat, but not exactly, as those of a Hammond B3 with
percussion on and at fast decay.This
effect applied only to the flute tone pickups.

Another
interesting and musically enhancing effect is that of chorusing or
celesting.It is physically
impossible to tune these reeds to 100% dead true accuracy.They can be, and indeed they are, tuned very closely and very
accurately, but they are all mechanically independent and unsynchronized.Additionally, each reed's electrical output waves contain true
harmonics.Therefore, a
subtle chorusing or celeste effect develops in the Wurlitzer electrostatic
whenever two or more tones get played simultaneously.This occurs not only through the minute tuning imperfections of the
reeds, but also because of the difference between the pitches of the
tempered notes of the musical scale and the true harmonics of the
generated tones.

Whenever
the various slight tuning imperfections between the fundamentals and
harmonics of the reeds interact with each other, this exactly parallels
what happens in real (acoustic) musical instruments, choirs of singers,
and orchestras where an infinite and constantly changing array of minute
tuning imperfections exist all the time.

At
some point during the production of these instruments, Wurlitzer made a
major change in the layout of the reed unit and the blower location.The pictures which we show here are from the newer version.In the older version, the reed pans were stacked in two tiers, one
over the other, and the blower was on the back of the reed unit.Since the whole assembly had to fit in the console, the blower was
placed with its shaft at right angles to the keyboards, which meant that
the blower motor had to drive the blower impeller by means of a
right-angle gear assembly.This
was an extra complication and also a source of mechanical noise.

By
1956, the reed unit had been redesigned to the configuration which we show
in these pictures, with all the reed pans on the same level, and the
blower assembly on the top.The blower is in line with the motor, which eliminates the
need of a right-angle gear unit and its resulting noise and also its
requirement for periodic lubrication, which, because of its location in
the early version necessitated removal of the reed unit from the console.In the newer version, motor and blower oiling holes are easily
accessible with removal of the console back, and the front soundproofing
panel of the reed unit housing.

If
you look at some of the pictures of the reeds, you will notice that all of
the reeds are wired together.This
provides a common signal output.Even
though the reeds produce many different frequencies and up to three
different waveforms, these may all be combined and still retain their
individual identities.If
this seems hard to believe at first, think of your stereo or hi-fi sound
system.All of the sounds of
a complete symphony orchestra combine over just two wires from your
amplifier outputs to your speakers.Thus,
all these different frequencies and waveforms can combine into a single,
complex alternating current audio signal and yet we can still pick out
individual instruments, singers, etc.when we listen to the sounds from the speakers of our stereos.

Therefore,
it comes as no surprise that Wurlitzer could combine the outputs of all of
the reeds.In actuality, the
first 24 bass reeds are commoned as one group and their signals go to one
input on the amplifier designated as the bass channel.The remaining reeds are combined in a different group and their
signals go through a separate input stage with much better treble response
and also high-pass filtering to suppress low-frequency keying transients
which result from the keying networks when in the fast percussion mode and
which would otherwise give audible thumps and thuds in the music.These thumps are not a problem in the bass tones, however, since
the bass tones are themselves low frequencies, and the percussion fast
attack effect is not available on the bass pedal tones anyhow.

The
voltages in most electrostatic transducer systems such as the Wurlitzer
reed unit are relatively high, and the resistances are also extremely
high, resulting in extremely minute audio signal current flows, down in
the micro amp range.Because
of this, in damp weather, enough of the high voltage DC from the keying
circuits can leak through the surrounding air to leave a slight charge on
the reed pickups.This
results in the continuous production of all of the tones of the
instrument.In order to
reduce or eliminate this problem, a slight positive bias voltage can be
applied to the reeds.A
variable resistor in the console controls this bias voltage and is
adjustable by turning the slotted movable contact or so-called
"wiper" of this variable resistor.

When
the bias on the reeds equals the leak voltage on the pickups, there is no
longer any net voltage difference between idle pickups and the reeds.Subsequently, the spurious background tones disappear.Because there is DC present on the reeds, it is necessary to
confine this DC to the reeds and allow only the alternating current audio
signals to proceed from the reeds to the input of the organ amplifier.Although this bias is adjustable, and may at times be tweaked very
low, there is also an essentially constant DC voltage on the grids of the
preamplifier input tubes.Electrical separation of these DC voltages is accomplished by
inserting a blocking capacitor in the signal path.

The
actual audio signal of all the reeds in either the bass or treble group
develops across a very high value resistive load.Remember when I said we needed to insert a load resistor in the
circuit in order to get a usable AC audio signal from a vibrating
capacitor? In these instruments, there are two resistors in series with
the shallots of all the reeds of a group and ground.Their values are 9,100,000 and 3,900 ohms.[The bias voltage is applied at the point between the two.] At the
top end of the 9,100,000 ohm resistor, there is a blocking capacitor, the
other end of which goes through a 1,000,000 ohm load resistor, from which
the signal develops and then passes to the grid of the first or
preamplifying tube in the amplifier section of the instrument.

Recall
earlier that we said an alternating current can effectively appear to flow
through a capacitor.Direct
current, however, only flows in briefly until the capacitor is charged, at
which point no more direct current can flow.For the purposes of an amplifier input such as the input stages of
the Wurlitzer amplifier, we can therefore think and say that the input
capacitor allows the AC audio signal to flow through itself.The end result of this is simply that the signal, which is AC, gets
by the blocking capacitor and appears on the grid of the input tube,
whereas the DC from the bias and any stray leakage cannot get through.

This,
then is yet another function of a capacitor in an amplifier; to allow the
AC signal to affect subsequent parts of the amplification circuitry, but
to keep any DC from getting through.In this function, a capacitor may be called either a coupling or a
blocking capacitor.In
subsequent sections of the Wurlitzer amplifier, and indeed in all
amplifiers, numerous internal capacitors allow AC signals to flow but
block DC operating or bias voltages.

There
is still another very important function in these amplifiers which is also
a capacitor-based function, and that is power filtering.Since the power that we all use is alternating current, typically
at 60 cycles in the USA and 50 cycles in Europe, we have to convert it to
DC before we can use it for our amplifiers, musical instruments, and these
days, for computers and other digital devices.This conversion is accomplished by a device called a rectifier,
which, for our purposes, we can simply say turns every negative half of
the input AC into a positive pulse and sends it along with the positive
halves to the next part of the amplifier.

This
seems simple enough, but if we consider ordinary 60 cycle AC, we need to
realize that each cycle consists of a positive pulse followed by a
negative pulse of power.These two pulses constitute a cycle.With a frequency of 60 cycles per second, this gives us 120
power pulses per second.One
hundred-twenty cycles per second is a little bit lower than the note B
right below Tenor C on the keyboard.If we ran this into our Wurlitzer electrostatic organ, we'd hear an
overwhelming buzz that would obliterate any and all possible musical
signals.

Therefore,
we must filter the rectified but pulsating direct current that the
rectifier circuit gives us.This
we can accomplish by placing several large capacitors in the circuit just
after the rectifier.As the
voltage of each power pulse builds, it charges these capacitors.When it decreases and momentarily drops to zero between pulses, the
capacitors give back stored power from the previous pulse to the
subsequent circuitry.To make
the filtering really effective, several capacitors follow each other, with
either low value resistors or coils of wire called filter chokes between
them.

At
the input of such a filtering network we have a 120 cycle pulsating direct
current.At the output, we
have a steady, non-pulsating smooth DC which we can use for powering all
of the subsequent electronic circuits, for charging the pickups on the
reeds, and for anything else that is needed in the tone producing or
amplification portions of the instrument.The main organ transformer, the rectifier, and the subsequent
filtering capacitors constitute the power supply of the organ.In the electrostatic Wurlitzer, this power supply is incorporated
into the main amplifier chassis that you see in the picture of the general
console layout.

A
second really important part of this amplifier chassis is the vibrato
system.Because the reeds are
essentially constant frequency devices, there is no practical way to
introduce a pitch-varying vibrato directly at the reeds.Cyclically varying the operating air pressure to free reeds
primarily changes their loudness or vibration amplitude, but produces an
almost negligible pitch change.Yet,
the Wurlitzer electrostatic organs do indeed produce a true
frequency-modulating vibrato in a rather ingenious manner.

In
the amplifier, all frequencies except for the lowest twenty four can go
through a special circuit which by means of a vacuum tube and a pair of
resistor-capacitor networks splits the signal into two signals which are
always ninety degrees out of phase with each other.Refer to the preliminary discussion on phase.

Associated
with this network are two variable gain gating circuits which work in
opposition and whose gain is cycled at the vibrato rate.Thus, the instantaneous signal constantly changes phase by ninety
degrees, retarding in phase and then smoothly advancing.A change in phase produces a change in frequency as I mentioned in
the preliminary section.Therefore,
by continually making first one and then the other gating circuit conduct
and having one gradually conduct less while the other conducts more, the
circuit constantly and smoothly advances and retards the phase by ninety
degrees of all electrical signals that are fed into it, in this case, the
signals from all of the reeds from #25 to # 85.Thus results in a true frequency modulation or vibrato in the
signal.

The
Wurlitzer electrostatic organ vibrato, however, was not as full and rich
sounding as that of the Hammond, and thus Ken also used a Leslie speaker
to add its characteristic acoustic vibrato-tremolo to the instrument's
tones.This you can hear in
many of the selections on his record, 67 Melody Lane.

On
his recordings, Ken did not use the full potential of the electrostatic
organ's available percussion effects.I believe that this was not due to any lack of musicianship on
Ken's part, because in many of his recordings he demonstrates a great deal
of creative ability, but rather upon the limitations of the recording
equipment as it existed when he made most of his recordings.The electrostatic organ tended to introduce a very low frequency
thud into the attacks of its tones when in the percussion fast-attack
mode.While these thuds would
be low enough in pitch not to intrude on the music, they might present
very real and high amplitude excursions into the audio voltage, and the
resulting keying transients on an LP record could very likely cause the
groove deviations to be large enough to cause cross-overs between adjacent
grooves.Of course, it could
also have been just that the percussive fast-attack circuitry had not yet
been made available when Ken made his recordings.